Method for establishing a path for a vehicle

ABSTRACT

A method for a follower vehicle following a lead vehicle, comprising establishing, in a first control mode of the follower vehicle, a path for the follower vehicle to follow the lead vehicle, characterized by
         generating environmental data which is related to the environment of the lead vehicle,   determining, based on the generated environmental data, an expected behaviour of an operational parameter of the lead vehicle,   determining an actual behaviour of the lead vehicle operational parameter,   comparing the determined expected behaviour of the lead vehicle operational parameter and the determined actual behaviour of the lead vehicle operational parameter,   determining based on said comparison whether to continue in first control mode of the follower vehicle, or in a second control mode of the follower vehicle, differing from the first control mode.

This application is a 35 USC 371 national phase filing of International Application No. PCT/EP2018/079940, filed Nov. 1, 2018, which claims the benefit of International Application No. PCT/EP2018/062188, filed May 11, 2018, the disclosures of which are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The invention relates to a method for a follower vehicle following a lead vehicle. The invention also relates to a computer program, a computer readable medium, a control unit and a vehicle.

The invention can be applied in heavy-duty vehicles, such as trucks and buses. Although the invention will be described with respect to trucks, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as cars.

BACKGROUND

A follower vehicle following, e.g. by means of vehicle-to-vehicle (V2V) communication, a lead vehicle, may in some cases be referred to as autonomous vehicle following, or auto-following. Such following could be applied to a string of vehicles, comprising the lead vehicle and the follower vehicle following the lead vehicle, e.g. by means of V2V communication. V2V communication involves information sent between a vehicle, and one or more surrounding vehicles, over a wireless communication channel. In addition to V2V communication, the follower vehicle could follow the lead vehicle by means of sensors, e.g. object sensors, such as radar, camera, and/or lidar.

Autonomous vehicle following allows the removal of the driver from the follower vehicles and have the vehicles follow the lead vehicle fully automatically. Thereby, in addition to longitudinal follower vehicle control, an automatic lateral follower vehicle control is used. For example, in a string, there may be a control of the longitudinal movements of the follower vehicle, as well as the lateral movements of the follower vehicle. A follower vehicle following the lead vehicle in a string, may in some cases be referred to as driver-less platooning. Driverless follower vehicles allow for cost reductions, and the removal of the “human factor” which may provide increased safety.

The longitudinal control of the follower vehicle could be provided by means of Cooperative Adaptive Cruise Control (CACC). In platooning, e.g. by means of CACC, vehicle convoys are driven with short distances between the vehicles, whereby the vehicles form a string.

The string may be formed of a row of vehicles, one following another. To achieve this with a high safety, a control unit of each vehicle may receive information from surrounding vehicles via V2V communication. For example, such shared information may include brake pressure, engine torque, engine RPM, accelerator pedal position, engine manifold pressure, vehicle speed, brake pedal position, vehicle acceleration, and/or radar/lidar data. Thus, it is understood that the V2V communication may provide for controlling the velocity and/or acceleration of a vehicle the string in dependence on the signals received from another vehicle in the string.

Alternatively, the longitudinal control of the follower vehicle could be provided by means of Adaptive Cruise Control (ACC). More generally, a string does not necessarily have to involve CACC, but can involve some other technology for longitudinal control of the follower vehicle(s).

Benefits with platooning include increased fuel efficiency, provided by a reduced air-drag due to short distances between vehicles, and provided by improved vehicle control due to more accurate information about the preceding vehicle. A further benefit is an improved traffic flow due to the small delay of the V2V data. More specifically, an improved traffic flow is provided by reducing the distance between vehicles, and avoiding “rubber-band” effects between vehicles, this being enabled by the small delay in V2V data.

The lateral control of the follower vehicle could be provided by means of position coordinates received from the lead vehicle. The position coordinates may be sent by V2V communication. The lateral control of the follower vehicle could also be provided by means of the Global Navigation Satellite System (GNSS), e.g. using the Global Positioning System (GPS). In some cases, the lateral control may be provided by means of sensors, e.g. by finding the rear-most part of the vehicle ahead and tracking it.

US2013090802 describes path estimation for autonomous vehicle following based on the acquisition of waypoints associated with a leader. The acquired waypoints may be pre-processed, including for example filtering, interpolation and cropping, to improve accuracy and then spline fitted to define a following path that is calculated to estimate the traversed path of the leader. The autonomous following vehicle may then be driven along the calculated path.

Notwithstanding said benefits, there is still room for improvement of known autonomous vehicle following strategies.

SUMMARY

An object of the invention is to increase the safety in autonomous vehicle following. Another object of the invention is to simplify autonomous vehicle following.

The objects are reached with a method for a follower following a lead vehicle, comprising establishing, in a first control mode of the follower vehicle, a path for the follower vehicle to follow the lead vehicle, the method comprising

-   -   generating environmental data which is related to the         environment of the lead vehicle,     -   determining, based on the generated environmental data, an         expected behaviour of an operational parameter of the lead         vehicle,     -   determining an actual behaviour of the lead vehicle operational         parameter,     -   comparing the determined expected behaviour and the determined         actual behaviour of the lead vehicle operational parameter,     -   determining based on said comparison whether to continue in         first control mode of the follower vehicle, or in a second         control mode of the follower vehicle, differing from the first         control mode.

The method may be carried out by the follower vehicle. Some, or all, of the data used in the method may be determined by the lead vehicle, and communicated to the follower vehicle via V2V communication.

The environmental data may include surroundings data, regarding the surroundings of the lead vehicle and/or the follower vehicle, e.g. environmental conditions, or upcoming objects detected by one or more sensors of the lead vehicle. In addition, or alternatively, the environmental data may include road data, including one or more features of a road on which the vehicles are travelling, e.g. the road condition, the road type, such as whether the road is a motorway, or a street in a city, the curvature of the road at one or more locations of the road, the inclination of the road at one or more locations of the road, or the speed limit at one or more locations of the road. The environmental data may include information on a stretch of the road on which the lead vehicle is travelling, at, e.g. in front of and/or laterally of, the lead vehicle. The environmental data may include information about road surface markings at, e.g. in front of or laterally of, the lead vehicle. The environmental data may include information about the location and/or the orientation of the lead vehicle in relation to road surface markings at the lead vehicle. The environmental data may be obtained from map data, and/or sensor data. The environmental data may be obtained by means of one or more sensors, e.g. one or more cameras, radar sensors, and/or LIDAR sensors, on the lead vehicle. Where a plurality of sources are used to determine the environmental data, a mathematical filter, such as a Kalman filter, may be used to establish their respective influence on the environmental data. In some embodiments, a Kalman filter may be used to establish the common influence, of the data from the sources, on the environmental data.

The operational parameter may be a lead vehicle control parameter related to the control of the lead vehicle, such as the steering angle, an accelerator control setting, or a brake control setting. Such control may be manual or automatic. In some embodiments, the operational parameter may be related to the behavior of the lead vehicle, such as the lead vehicle speed, the lead vehicle acceleration, the lead vehicle yawrate, the lead vehicle lateral position, or the lead vehicle lateral acceleration. In some embodiments, the lead vehicle operational parameter may be an aggregation of two or more further lead vehicle operational parameters.

The operational parameter behavior may be, for example, one or more values of the operational parameter in relation to a threshold value, or the change of the operational parameter values over time, or over distance travelled by the lead vehicle.

The actual behaviour of the lead vehicle operational parameter may be determined by the lead vehicle. The actual behaviour of the lead vehicle operational parameter may be communicated to the follower vehicle by V2V. The actual behaviour of the lead vehicle operational parameter may be determined by means of driver input information. Thus, the lead vehicle operational parameter may be a lead vehicle control parameter. Alternatively, or in addition, the actual behaviour of the lead vehicle operational parameter may be determined by means of a sensor, e.g. a radar sensor, on the follower vehicle.

The method may comprise comparing the determined actual behaviour of the lead vehicle operational parameter to the determined expected behaviour of the lead vehicle operational parameter. The actual lead vehicle operational parameter behaviour and the expected lead vehicle operational parameter behaviour may agree with each other such that it is determined that the follower vehicle should continue to be controlled in the first control mode. However, the actual lead vehicle operational parameter behaviour may subsequently deviate from the expected lead vehicle operational parameter behaviour such that it is determined to change the control of the follower vehicle from the first control mode to the second control mode.

In some embodiments, the first control mode of the follower vehicle control may be kept active when the actual lead vehicle operational parameter behaviour deviates from the expected lead vehicle operational parameter behaviour. Thereby, the actual lead vehicle operational parameter behaviour and the expected lead vehicle operational parameter behaviour may subsequently agree with each other such that it is determined to change the control of the follower vehicle from the first control mode to the second control mode. The method provides for obtaining clear values of the lead vehicle operational parameter, which can be easily and quickly compared to each other. Thereby, a possibility to quickly adjust a selection of the follower vehicle control mode, e.g. depending on the changing control profile of the lead vehicle, is provided. Thereby, the safety in autonomous vehicle following may be increase in a way that is simple to implement.

Preferably, determining the expected behavior of the lead vehicle operational parameter comprises determining an interval of the operational parameter, and comparing, the determined expected behaviour and the determined actual behaviour of the lead vehicle operational parameter, comprises determining whether an actual value of the operational parameter is within the operational parameter interval. The expected behavior of the lead vehicle operational parameter may be determined, e.g. by means of a driver model, and/or a lead vehicle model. The operational parameter interval may represent an expected normal, or nominal, driving profile. The interval may allow for an expected variety of driving profiles, which profiles may differ from one driver to another. The actual value of the operational parameter being outside of the operational parameter interval may be quickly established, whereby a possibility to quickly adjust a selection of the follower vehicle control mode is provided. Thus, the interval provides a manner to perform the method, which is simple to implement.

As exemplified below, the environmental data may comprise speed limit data. The speed limit data is preferably speed limit data concerning the road on which the lead vehicle is travelling. The method may thereby, by involving the actual lead vehicle speed, or acceleration, provide a simple manner of deciding whether to adjust a selection of the follower vehicle control mode.

In some embodiments, the environmental data may comprise a curvature of the road on which the lead vehicle is travelling. Thereby, the lead vehicle operational parameter may be a steering angle of the lead vehicle. In some embodiments, a lead vehicle model may be used to determine, based on the road curvature, the expected lead vehicle steering angle. Thereby, an effective manner of determining whether the lead vehicle deviates from a normal behavior of driving within a lane, at a speed which is adapted to the road curvature, may be provided. Further examples of suitable lead vehicle operational parameters include the lead vehicle yawrate, the lead vehicle longitudinal acceleration, and the lead vehicle lateral acceleration.

The first control mode may comprise, as also described below, determining a position and a heading of the lead vehicle, determining a position and a heading of the follower vehicle, subsequently establishing a path for the follower vehicle by fitting a curve to said positions and said headings, and controlling the follower vehicle so as to move along the established path. The second mode may comprise, as exemplified below, determining a plurality of positions of the lead vehicle as the lead vehicle moves, and establishing a path for the follower vehicle by fitting a curve to at least some of the plurality of lead vehicle positions.

The first mode may thereby provide a smoother path for the follower vehicle, whereas, the second mode may provide a more exact following of the leader vehicle. Changing from the first mode to the second mode may be beneficial, e.g. in cases where a difference between the actual behavior and the expected behavior, of the operational parameter, is caused by an unexpected event in the conditions of the leader vehicle, such as an obstacle which the lead vehicle needs to avoid. In such cases, a close following of the leader vehicle, provided by the second mode, may be preferred.

The objects are also reached with a method for a follower vehicle following a lead vehicle, comprising

-   -   determining a position and a heading of the lead vehicle,     -   determining a position and a heading of the follower vehicle,     -   subsequently establishing a path for the follower vehicle by         fitting a curve to said positions and said headings,     -   and controlling the follower vehicle so as to move along the         established path.

The lead vehicle may drive ahead of the follower vehicle. The follower vehicle's following of the lead vehicle may be an autonomous vehicle following. The method may involve a plurality of follower vehicles following the lead vehicle.

The determined heading of the lead vehicle is preferably at the determined position of the lead vehicle. The determined heading of the follower vehicle is preferably at the determined position of the follower vehicle.

Determining the positions and headings of the lead vehicle and the follower vehicle may involve determining the absolute position and the absolute heading of the lead vehicle. Determining the positions and headings of the lead vehicle and the follower vehicle may involve determining the absolute position and the absolute heading of the follower vehicle. However, in some embodiments, the determined position of the lead vehicle may be the lead vehicle position in relation to the follower vehicle position. In some embodiments, the determined heading of the lead vehicle may be the lead vehicle heading in relation to the follower heading. The path may be calculated based on the follower vehicle's position and heading to the lead vehicle's position and heading.

Embodiments of the invention provides for establishing said path for the follower vehicle by fitting the curve to said positions and said headings, after said positions and said headings have been determined. The curve fitted to said positions and said headings may be a smooth curve. The curve may take the follower vehicle from its position and heading to the lead vehicle's position and heading.

The position and a heading of the lead vehicle may, for example, be acquired by means of the Global Navigation Satellite System (GNSS), e.g. using the Global Positioning System (GPS). The position and a heading of the lead vehicle may be sent from the lead vehicle to the follower vehicle via V2V communication. Thus, the follower vehicle may receive information relating to the position coordinates and the heading of the lead vehicle. In some cases, the position and a heading of the lead vehicle may be provided by means of sensors of the follower vehicle, for example object sensors tracking the lead vehicle.

The position and the heading of the lead vehicle may be determined at the same time. Herein, the lead vehicle position and heading, determined at the same time, are jointly referred to as a lead vehicle position and heading data set. The position and the heading of the follower vehicle may be determined at the same time. Herein, the follower vehicle position and heading, determined at the same time, are jointly referred to as a follower vehicle position and heading data set. Further, the lead vehicle position and heading data set, and the follower vehicle position and heading data set, may be determined at substantially the same time. In some embodiments, the follower vehicle position and heading data set is determined when the lead vehicle position and heading data set is received by the follower vehicle.

Preferably the position of the lead vehicle is a position of a reference point of the lead vehicle. Preferably, the lead vehicle reference point is fixed in relation to the lead vehicle. Preferably, the lead vehicle reference point is located at a front axle of the lead vehicle. Preferably the position of the follower vehicle is a position of a reference point of the follower vehicle. Preferably, the follower vehicle reference point is fixed in relation to the follower vehicle. Preferably, the follower vehicle reference point is located at a front axle of the follower vehicle. Where the lead vehicle and the follower vehicle form parts of a string, each vehicle in the string may present a reference point, the position of which indicates the position of the respective vehicle.

Preferably, the reference points of the vehicles are at the same relative position in the respective vehicle, for example at the respective front axle. Thereby, the vehicle motion patterns may be the same. In some embodiments, the method can comprise determining the position of a preliminary point on the lead vehicle. Thereby, determining the position of the lead vehicle may comprise determining the position of the lead vehicle reference point based on the position of the lead vehicle preliminary point and a known spatial relationship between the preliminary point and the reference point. Similarly, the method can comprise determining the position of a preliminary point on the follower vehicle, wherein determining the position of the follower vehicle may comprise determining the position of the follower vehicle reference point based on the position of the follower vehicle preliminary point and a known spatial relationship between the preliminary point and the reference point.

It should be noted that, as the follower vehicle follows the lead vehicle, as the latter is moving ahead, steps of the method may be repeated. Thereby a plurality of sequential positions and headings of the lead vehicle may be determined. Further, a plurality of sequential positions and headings of the follower vehicle may be determined. In some embodiments, after each determination of the lead vehicle's position and heading, and after each determination of the follower vehicle's position and heading, a path for the follower vehicle is established by fitting a curve to the determined positions and headings. Thereby, a sequence of paths may be created as the vehicles move along. Thus, as the vehicles move along, the positions and headings of lead vehicle and follower vehicle may be repetitively updated, and the follower vehicle path may be repetitively updated.

The invention makes it possible to establish the path for the follower vehicle without data on the lead vehicle movement history. Instead the path may be established based on the present position and a heading of the lead vehicle. This provides significant advantages compared to said known method in US2013090802, where a path estimation is based on the acquisition of waypoints associated with a leader. In the known method, the estimated path will depend on the route that the lead vehicle has taken to its present position. The invention allows for choosing the path without any consideration for such a historical lead vehicle route. This provides a more flexible path choice, which is beneficial, in particular where the surroundings involve relatively large amounts of free space around the vehicles. Such surrounds may occur for example on a motorway, or in a truck loading area, e.g. in a container shipping harbor. The invention provides an improved performance by balancing the need for accuracy in vehicle following, with smoothness in the control.

By the invention it is possible to avoid, where not necessary, the follower vehicle mimicking everything the lead vehicle is doing. For example, where the lead vehicle is driven by a person who controls the lead vehicle so as to sway as it is moved forward, the invention may provide for the follower vehicle to create, while still following the lead vehicle, its own path so as to avoid the swaying. Thereby, safety in autonomous vehicle following is increased.

Further the invention allows for the amount of data transferred from the lead vehicle to the follower vehicle to be considerably reduced. More specifically, updating the position and heading of the lead vehicle may require a considerably reduced bandwidth, compared to the known method with path estimation based on waypoints. In particular, the frequency of the data transfer may be reduced significantly. Thereby, autonomous vehicle following may be simplified.

In some embodiments, a plurality of follower vehicles may follow a lead vehicle. Thereby, a position and a heading of an additional follower vehicle may be determined, wherein subsequently a path for the additional follower vehicle is established by fitting a curve to the position and heading of the lead vehicle and the position and heading of the additional follower vehicle. Thereby, the additional follower vehicle may be controlled so as to move along the established path. Alternatively, or in addition, a follower vehicle, herein referred to as a first follower vehicle, may fill the role of a lead vehicle for an additional follower vehicle, in that a position and a heading of the first follower vehicle is determined, a position and a heading of the additional follower vehicle is determined, subsequently a path for the additional follower vehicle is established by fitting a curve to said positions and said headings, and the additional follower vehicle is controlled so as to move along the established path. For example, the first follower vehicle may fill the role of a lead vehicle, where the additional vehicle, for some reason, doesn't receive data from the lead vehicle for the first follower vehicle.

Preferably, the curve fitting comprises creating the curve so as to be tangential to each of said headings at a respective of said positions. Thereby, a smooth path, guiding the follower vehicle to the present position and heading of the lead vehicle, may be created. Preferably, the curve is a polynomial of a degree of at least three. This allows creating a path with a portion having a curvature in one direction, and another portion having a curvature in the other direction. Thereby, paths taking the follower vehicle between a variety of relative positions and headings are allowed.

In some applications of the invention, the lead vehicle is standing still, when the path for the follower vehicle is established. Thereby, the invention could be advantageously applied to a situation where a string of platooning vehicles is to be formed. The lead vehicle may be driven by a driver. The follower vehicle may be an autonomous follower. During an initiation of the string the lead vehicle may be standing still. Thereby, the heading of the lead vehicle may have been determined when the lead vehicle was in a transition from moving to standing still. The heading of the lead vehicle may be stored, e.g. by a control unit of the lead vehicle. After receiving the position and the heading of the lead vehicle, and after having determined the position and heading of the follower vehicle, the follower vehicle may establish the path for the follower vehicle by fitting a curve to said positions and said headings. Thereupon, the follower vehicle may be controlled so as to move along the established path. Thereby, the follower vehicle may move so as to end up behind the lead vehicle. Thereby, the follower vehicle may move so as to end up behind the lead vehicle, and having substantially the same heading as the lead vehicle. The follower vehicle may park behind the lead vehicle.

This enables a possibility of initializing an auto-follower platoon without the need for drivers in the follower vehicles at any stage during the initiation. In some implementations, a plurality of follower vehicles may line up behind a lead vehicle. Thereby, a first follower vehicle may fill the role of a lead vehicle for an additional follower vehicle, in that a position and a heading of the first follower vehicle is determined, a position and a heading of the additional follower vehicle is determined, subsequently a path for the additional follower vehicle is established by fitting a curve to said positions and said headings, and the additional follower vehicle is controlled so as to move along the established path.

It should be noted that, advantageously, embodiments of the invention allow the follower vehicle to arrive behind the lead vehicle, without having followed the same path as the lead vehicle, or even having arrived from the same direction as the lead vehicle.

In some applications of the invention, the lead vehicle may, during an initiation of the string, be driving, e.g. slowly or at a relatively high speed. Thereby, the follower vehicle, which is to form a string with the lead vehicle, and possibly other follower vehicles, may be driving at a distance from the lead vehicle, which is larger than the distance between the vehicles when the string is formed. After receiving the position and the heading of the lead vehicle, and after having determined the position and heading of the follower vehicle, the follower vehicle may establish the path for the follower vehicle by fitting a curve to said positions and said headings. Thereby, the follower vehicle may move so as to end up behind the lead vehicle, and having substantially the same heading as the lead vehicle.

In some embodiments, said path is established in a first control mode of the follower vehicle,

-   -   the method further comprising generating operational data which         is at least partly related to the operation of the lead vehicle,     -   and determining based on the operational data whether to control         the follower vehicle in the first mode, or in a second mode,         differing from the first mode.

The second mode may comprise determining a plurality of positions of the lead vehicle as the lead vehicle moves, and establishing a path for the follower vehicle by fitting a curve to at least some of the plurality of lead vehicle positions. Thus, the first mode may involve controlling the follower vehicle so as to move along a path established by fitting a curve to positions and headings of the lead vehicle and the follower vehicle. The second mode may involve controlling the follower vehicle so as to move along a path established by fitting a curve to at least some of a plurality of lead vehicle positions. Such lead vehicle positions are herein also referred to as waypoints. Thus, in the second mode, the follower vehicle may follow a trail created by the lead vehicle.

Thereby, a possibility to select the first or the second mode, e.g. depending on the operational data is provided. For example, the operational data may comprise environmental data, as also exemplified above. The environmental data may comprise surroundings data, and/or road data. Thus, the operational data may include surroundings data, regarding the surroundings of the lead vehicle and/or the follower vehicle, e.g. environmental conditions, or upcoming objects detected by one or more sensors of the lead vehicle. The operational data may include road data, including one or more features of a road on which the vehicles are travelling, e.g. the road condition, the road type, such as whether the road is a motorway, or a street in a city, the curvature of the road at one or more locations of the road, the inclination of the road at one or more locations of the road, or the speed limit at one or more locations of the road. The road data may be obtained from map data, and/or sensor data. The surroundings data and the road data are herein also referred to as environmental data. The operational data may include one or more values of one or more operational parameters of the lead vehicle. The one or more lead vehicle operational parameters may include one or more lead vehicle control parameters. Thus, the operational data may include one or more values of one or more lead vehicle control parameters, related to the control of the lead vehicle, such as the steering angle, an accelerator control setting, or a brake control setting. The operational data may include lead vehicle driver data, regarding lead vehicle control actions initiated by a driver of the lead vehicle, for example driver input data, and/or data regarding the lead vehicle driver condition. One or more values of one or more lead vehicle operational parameters could form at least a part of the lead vehicle driver data. The operational data, for example lead vehicle operational parameter values thereof, could include the lead vehicle movement, such as the lateral acceleration and/or the yaw rate thereof. The operational data may include data generated by the lead vehicle, the follower vehicle, or a vehicle ahead of the lead vehicle.

Thus, in the second mode, the exact behavior of the lead vehicle may be replicated by the follower vehicle. This may be advantageous in some circumstances. However, in other circumstances it may be more beneficial that a track between the two vehicles, determined based on the positions and heading of the vehicles, is followed by the follower vehicle. Thus, when a situation is assessed, a fitting lateral control strategy may be chosen.

For example, lead vehicle driver data, based on lead vehicle speed and lead vehicle steering wheel movements, combined with surroundings data and road data, could indicate that the lead vehicle driver is swerving often without this being called for by the conditions. Such swerving could be an indication of a “nervous” driving behavior of the lead vehicle, which is not wanted in the follower vehicle. In such an example, it may be determined to control the follower vehicle in the first mode. This may give a calm and comfortable control of the follower vehicle in a situation where a certain deviation from the lead vehicle path is acceptable. Thereby, the lead vehicle might sway a bit back and forth within the lane, e.g. due to it being driven by a human driver. The follower vehicle may thereby smoothen out that swaying and can attempt a straighter line reducing the swaying.

However, if road data and/or surroundings data indicate that the follower vehicle is in a relatively narrow situation, such as in a roundabout, a motorway exit, or a sharp curve, on a narrow and/or curvy road, such as a rural road, it may be vital that a movement of the lead vehicle is at least substantially replicated. The follower vehicle control may want to ensure that the follower vehicle is not cutting any corner. In such a case, it may be determined to control the follower vehicle in the second mode.

Thereby, a flexible control of the follower vehicle is provided, allowing fully automated following in a variety of situations, which may occur, e.g. in a hub-to-hub scenario, where some part of a trip is more narrow and curvy than others. Thus, operational conditions may be registered or analyzed to form operational data, and the mode for the lateral control strategy of the follower vehicle may be selected based on the operational data. This may be done continuously or repetitively, so that each time the operational conditions change, the lateral control strategy is changed accordingly.

It should be noted that in some embodiments, the second mode may be adjusted, so that instead of following exactly in the track of the lead vehicle, the path established for the follower vehicle could be an approximation of said track, e.g. by fitting a curve to less than all of the plurality of lead vehicle positions. In some embodiments, the second mode adjustment could include adjusting the number of lead vehicle waypoints used for the curve adaption for the path for the follower vehicle to follow. In some embodiments, the adjusted second mode comprises determining a plurality of positions of the lead vehicle as the lead vehicle moves, and establishing a path for the follower vehicle by fitting a curve to a number of the lead vehicle positions, which number is lower than the number of lead vehicle positions to which a curve is fitted in the un-adjusted second mode. Such an adjustment could be based on one or more differences between the lead vehicle and the follower vehicle, e.g. where the vehicles are of different types of tractor and trailer combinations. Thus, an adjustment of the second mode could be based on data regarding one or more properties and/or restrictions of the lead vehicle as well as the follower vehicle.

Preferably, at least one or more parts of the operational data is generated by the lead vehicle. Preferably, the operational data includes surrounding data generated by the lead vehicle. Preferably, at least one or more parts of the operational data is sent from the lead vehicle to the follower vehicle by vehicle-to-vehicle (V2V) communication. Thereby, the adaption of the path following algorithm to different scenarios is done by the vehicle that has the best knowledge about what kind of situation the vehicles are currently in, i.e. the lead vehicle. Thus, the current situation is preferably assessed by means of data from the lead vehicle. The operational data may include information provided by the lead vehicle such as information on one or more lead vehicle parameters, as exemplified below. The operational data may include information provided by the lead vehicle such as a message on one or more actions to prepare for lane change. The operational data may include lead vehicle movements, such as lateral acceleration, and/or yaw rate. The operational data may include one or more upcoming objects seen by lead vehicle, such as an obstacle in the way, that requires some sort of maneuver to avoid. The operational data may include driver input information, such as a steering wheel angle and/or torque. For example, if the lead vehicle driver puts in a lot of steering effort, indicated by a high steering wheel torque and/or a big angle on the steering wheel, a determination to control the follower vehicle in the second mode may be justified by stricter requirements on the follower vehicle to follow the lead vehicle more exactly, and on the follower vehicle control to be more active, e.g. “nervous”, to catch even small control adjustments of the lead vehicle.

Thus, in beneficial embodiments of the invention, during autonomous vehicle following, the path choice control strategy for a follower vehicle is adjusted based on data in the lead vehicle.

The operational data may be indicative of a change of a lead vehicle control strategy, from a first lead vehicle control strategy to a second lead vehicle control strategy, while the follower vehicle is controlled in the first mode, the method comprising determining, based on the operational data indicative of the lead vehicle control strategy change, to change to controlling the follower vehicle in the second mode.

The first and second lead vehicle control strategies may be first and second lead vehicle control profiles. The first lead vehicle control strategy may for example involve remaining in a road lane, and keeping the lead vehicle speed substantially constant, or within a speed interval, which may be predetermined. The second lead vehicle control strategy may be a driving maneuver. The driving maneuver may be a driving event. The driver maneuver may divert substantially from any driving control action in the first lead vehicle control strategy.

The operational data, based on which it is determined whether to control the follower vehicle in the first mode or in the second mode, may include one or more values of one or more operational parameters of the lead vehicle exceeding or being below a respective predetermined threshold value. The one or more lead vehicle operational parameter values, exceeding or being below a respective predetermined threshold value, may be indicative of a change of the lead vehicle control strategy. As stated, the one or more lead vehicle operational parameters may include one or more lead vehicle control parameters.

The one or more lead vehicle operational parameter may be the lead vehicle steering angle, the lead vehicle speed, the lead vehicle lateral position, the lead vehicle lateral speed, the lead vehicle longitudinal acceleration, and/or the lead vehicle yaw rate. In some embodiments, the one or more lead vehicle operational parameter values exceeding or being below a respective predetermined threshold value, may include a mean value, of a lead vehicle operational parameter, exceeding or being below a predetermined threshold value. In some embodiments, a lead vehicle operational parameter value, exceeding or being below a predetermined threshold value, may be a sum, of two or more further lead vehicle operational parameter values, exceeding or being below a threshold value.

In some embodiments, the operational data, based on which it is determined whether to control the follower vehicle in the first mode or in the second mode, may include data on a combination of substantially simultaneous events. Such a combination could be a combination of one or more of the following events: one or more values of one or more lead vehicle operational parameters, e.g. including one or more lead vehicle control parameters, being above or below respective a threshold value, lead vehicle braking, a lead vehicle gearshift, and map data, e.g. indicating an expected road intersection. The combination of substantially simultaneous events may be indicative of an obstacle in the road. The combination, of substantially simultaneous events, may be indicative of a change of the lead vehicle control strategy.

In some embodiments, the operational data, based on which it is determined whether to control the follower vehicle in the first mode or in the second mode, may include a pattern of a plurality of values of a lead vehicle operational parameter, such as a vehicle lateral position pattern, a vehicle speed pattern, or a steering angle pattern. The operational data, based on which it is determined whether to control the follower vehicle in the first mode or in the second mode, may include a change in the pattern of a plurality of values of a lead vehicle operational parameter. The change, in the pattern of a plurality of values of a lead vehicle operational parameter, may be indicative of a change of the lead vehicle control strategy. For example, if the pattern of the lead vehicle steering angle changes from relatively slow steering angle changes to relatively quick steering angle changes, this may be indicative of a change of the lead vehicle control strategy. As a further example, if the pattern of the lead vehicle speed changes from relatively slow speed changes to relatively quick speed changes, this may be indicative of a change of the lead vehicle control strategy.

As discussed below, the second lead vehicle control strategy may be an emergency maneuver, such as a maneuver to avoid an obstacle ahead of the lead vehicle. The second lead vehicle control strategy may alternatively be a standard maneuver of the lead vehicle, such as a lane change of the lead vehicle. Thereby, the choice between the first and second modes of controlling the follower vehicle, may be provided e.g. in a lane change situation, in which the follower vehicle control strategy selection may be important. A standard maneuver may be a type of non-emergency maneuver that is performed repetitively by a vehicle during its normal operation. Other examples, besides a lane change, may be driving through a tight curve, turning from one road onto another road, or driving through a roundabout.

In some embodiments, the operational data indicative of the lead vehicle control strategy change includes data based on a sensor of the lead vehicle. Thereby, an early indication of a change to a second lead vehicle control strategy, such as a lane change, may be provided. For example, the sensor may be a camera on the lead vehicle, by means of which the lateral position of the lead vehicle in the lane can be monitored. Data on the lateral position of the lead vehicle in the lane may be continuously or repetitively sent to the follower vehicle. The lead vehicle starting to leave the lane may indicate a lane change. By an early indication of a lane change of the lead vehicle, an early adaption of the follower vehicle control strategy may be provided.

The operational data indicative of the lead vehicle control strategy change may include data about a change, an activation, or a deactivation of a lead vehicle subsystem, such as a turn signal, or a gear shift. In some embodiments, the operational data indicative of the lead vehicle control strategy change includes data about a turn signal by the lead vehicle. Such data may be provided by means of V2V signals from the lead vehicle to the follower vehicle. Alternatively, or in addition, the turn signal data may be provided by means of a sensor on the follower vehicle. In some embodiments, a combination of a lead vehicle turn signal, and lane position information indicating that the lead vehicle is starting to leave the lane, may be required for a lane change situation to be identified.

In some embodiments, the operational data indicative of the lead vehicle control strategy change includes data about a planned route of the lead vehicle. Such data may require a lead vehicle turn signal, and/or lane position information indicating that the lead vehicle is starting to leave the lane, for a confirmation that a lane change situation is identified. In some embodiments, the operational data indicative of the lead vehicle control strategy change includes map data indicating an expected lead vehicle driving maneuver. Such indicative map data could be a road intersection, a roundabout, or a portion of the road having a relatively high curvature, or a relatively high inclination.

As stated, the second lead vehicle control strategy may be an emergency maneuver, such as a maneuver to avoid an obstacle ahead of the lead vehicle. Thus, the operational data may be indicative of an obstacle ahead of the lead vehicle, while the follower vehicle is controlled in the first mode, the method comprising determining, based on the operational data indicative of the obstacle, to change to controlling the follower vehicle in the second mode. Thereby, a change of the follower vehicle control strategy, so as for the follower vehicle to follow the lead vehicle more exactly, may be provided as a response to the obstacle detection. A close following of the lead vehicle path may be critical for the follower vehicle to avoid the obstacle. The data about the obstacle may be obtained by means of a sensor on the lead vehicle. The obstacle data may be sent by means of V2V communication from the lead vehicle to the follower vehicle. Thereby, an early indication of the obstacle is provided for the follower vehicle. Thus, an early adjustment of the follower vehicle control strategy, to adapt to the obstacle situation, may be provided.

The operational data may be indicative of the lead vehicle entering or driving on an off-ramp or an on-ramp at a motorway, while the follower vehicle is controlled in the first mode, and determining based on the operational data, indicative of the lead vehicle entering or driving on the off-ramp or the on-ramp, to change to controlling the follower vehicle in the second mode. Thereby, a change of the follower vehicle control strategy, so as for the follower vehicle to follow the lead vehicle more exactly, may be provided as a response to the lead vehicle entering or driving on an off-ramp or an on-ramp at a motorway. On such a ramp, a close following of the lead vehicle path may be critical for the follower vehicle. The data about the off-ramp or the on-ramp may be obtained by means of GNSS. It should be noted that data on what type of road the vehicle is travelling on is also attainable from one or more on-board sensors, such as a camera and/or lidar.

In some embodiments, the method comprises establishing the path in the second mode while controlling the follower vehicle so as to move along the path established in the first mode. For example, the method may comprise determining a position and a heading of the lead vehicle, determining a position and a heading of the follower vehicle, subsequently establishing a path for the follower vehicle by fitting a curve to said positions and said headings, and controlling the follower vehicle so as to move along the established path, and simultaneously determining a plurality of positions of the lead vehicle as the lead vehicle moves, and establishing a path for the follower vehicle by fitting a curve to at least some of the plurality of lead vehicle positions. Thereby, a path estimation in one of the modes may be actively used, while the path estimation in the other mode is passive. Such a parallel path establishment may be used to verify the plausibility of the mode used. For example, while using the first mode, the difference between the trajectories of the paths of the modes may indicate whether a change to the second mode should be undertaken.

In some embodiments, the method comprises establishing the path in the first mode while controlling the follower vehicle so as to move along the path established in the second mode.

The objects are also reached with a method for a follower vehicle following a lead vehicle, comprising

-   -   establishing a path in a first control mode of the follower         vehicle,     -   and controlling the follower vehicle so as to move along the         established path,     -   the method further comprising generating operational data which         is at least partly related to the operation of the lead vehicle,     -   and determining based on the operational data whether to control         the follower vehicle in the first mode, or in a second mode,         differing from the first mode.

The method may be provided in any suitable embodiment, e.g. as exemplified herein. Thus, the operational data may include at least one of surroundings data, road data, and one or more values of one or more lead vehicle operational parameters. The operational data may comprise environmental data, which in turn may comprise surroundings data, and/or road data, as exemplified above, and below. The operational data may be indicative of a change of a lead vehicle control strategy. The operational data may include one or more values of one or more operational parameters of the lead vehicle exceeding or being below a respective predetermined threshold value. The operational data may include data on a combination of substantially simultaneous events. The operational data may include a pattern of a plurality of values of a lead vehicle operational parameter. The operational data may be indicative of an obstacle ahead of the lead vehicle.

The objects are also reached with a method for a follower vehicle following a lead vehicle, comprising the lead vehicle generating operational data which is at least partly related to the operation of the lead vehicle, and determining based on the operational data whether to control the follower vehicle in a first mode or in a second mode, the first mode comprising controlling the follower vehicle so as to move along a path established according to a first algorithm, the second mode comprising controlling the follower vehicle so as to move along a path established according to a second algorithm, which is different from the first algorithm.

It is understood that the second mode differs from the first mode. The adaption of the path following algorithm to different scenarios is thereby done by the vehicle that may have the best knowledge about what kind of situation the vehicles are currently in, i.e. the lead vehicle. Similarly to what has been mentioned above, in the second mode, the exact behavior of the lead vehicle may be replicated by the follower vehicle. This may be advantageous in some circumstances. However, in other circumstances it may be more beneficial that a track between the two vehicles, determined with less consideration for the exact lead vehicle track, is followed by the follower vehicle. Thus, when a situation is assessed, a fitting lateral control strategy may be chosen.

The operational data may include at least one of surroundings data, regarding the surroundings of the lead vehicle and/or the follower vehicle, road data, including one or more features of a road on which the vehicles are travelling, and lead vehicle driver data, regarding lead vehicle control actions initiated by a driver of the lead vehicle. The operational data may comprise environmental data, which in turn may comprise surroundings data, and/or road data, as exemplified above. At least one or more parts of the operational data may be sent from the lead vehicle to the follower vehicle by vehicle-to-vehicle (V2V) communication. The operational data may be indicative of a change of a lead vehicle control strategy, from a first lead vehicle control strategy to a second lead vehicle control strategy, while the follower vehicle is controlled in the first mode, and determining, based on the operational data indicative of the lead vehicle control strategy change, to change to controlling the follower vehicle in the second mode. The operational data indicative of the lead vehicle control strategy change may include data based on a sensor of the lead vehicle. Above, further examples are given of operational data, based on which it is determined whether to control the follower vehicle in the first mode or in the second mode.

In some embodiments, the first algorithm comprises determining a position and a heading of the lead vehicle, determining a position and a heading of the follower vehicle, and subsequently establishing a path for the follower vehicle by fitting a curve to said positions and said headings, the first mode comprising controlling the follower vehicle so as to move along the established path. In some embodiments, the second mode comprises determining a plurality of positions of the lead vehicle as the lead vehicle moves, and establishing a path for the follower vehicle by fitting a curve to at least some of the plurality of lead vehicle positions. In some embodiments, the first mode comprises determining a plurality of positions of the lead vehicle as the lead vehicle moves, and establishing a path for the follower vehicle by fitting a curve to a number of the lead vehicle positions, which number is lower than the number of lead vehicle positions to which a curve is fitted in the second mode. Thus, a mode change could include for example adjusting the number of lead vehicle waypoints used for a curve adaption for a path for the follower vehicle to follow.

The objects are also reached with a method for a follower vehicle following a lead vehicle, comprising generating operational data which is at least partly related to a future operation of the lead vehicle, and determining based on the operational data whether to control the follower vehicle in a first mode or in a second mode, the first mode comprising controlling the follower vehicle so as to move along a path established according to a first algorithm, the second mode comprising controlling the follower vehicle so as to move along a path established according to a second algorithm, which is different from the first algorithm. The operational data may relate to a stretch of a planned vehicle journey. The operational data may be at least partly based on map data. The operational data may be generated, or entered into a vehicle control unit, manually.

The objects are also reached with a computer program according to claim 21, a computer readable medium according to claim 22, a control unit or a group of control units according to claim 23, or a vehicle according to claim 24. In some embodiments, the method may be performed by a single control unit in one of the vehicles, and in other embodiments, the method may be performed by a group of control units distributed in the vehicles. Thereby, one of the vehicles may be the lead vehicle. In some embodiments, the method may be performed by an external control unit, which is separate from the vehicles.

Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

In the drawings:

FIG. 1 is a side view of vehicles in a string of platooning vehicles.

FIG. 2 is a diagram depicting steps in a method performed by the vehicles in FIG. 1.

FIG. 3 is a top view of two of the vehicles in FIG. 1, in a first mode of autonomous vehicle following.

FIG. 4 is a top view of the vehicles in FIG. 3, in a second mode of autonomous vehicle following.

FIG. 5 is a diagram depicting steps in a method according to an alternative embodiment of the invention.

FIG. 6 is a top view of two vehicles about to initiate a string of platooning vehicles.

FIG. 7 is a block diagram depicting steps in a method to control one of the vehicles in FIG. 6.

FIG. 8 is a diagram showing vehicle speed and accelerations as functions of distance travelled, in an example of a method according to a further aspect of the invention.

FIG. 9 is a block diagram depicting steps in the example described also with reference to FIG. 8.

FIG. 10 is a diagram showing vehicle steering angles as functions of distance travelled, in a further example of the method according to the further aspect of the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

FIG. 1 shows what is herein referred to as a lead vehicle 1, and follower vehicles 2, 3. In this example, the vehicles 1, 2, 3 are trucks with semitrailers. However, the invention is equally applicable to other types of vehicles, such as cars, buses and dump trucks.

Each of the vehicles 1, 2, 3 comprises equipment 101, 201, 301 for platooning. For longitudinal control, the vehicles comprise in this example equipment for Cooperative Adaptive Cruise Control (CACC). The platooning equipment includes means for wireless communication with a radio transmitter and a radio receiver for so called Vehicle-to-Vehicle (V2V) communication, and a data communication processing device which is arranged to communicate with a control unit 102, 202, 302 of a respective vehicle control system. The control units 102, 202, 302 are herein also referred to as a group of control units. The wireless communication could be based on any suitable industry standard format, such as DSRC (Dedicated Short Range Communications), WiFi, radio modem, or Zigbee. This wireless communication could alternatively be based on a non-industry standard format. The means for wireless communication is in this example also used for lateral control of the follower vehicles 2, 3.

The lead vehicle 1 and the follower vehicles 2, 3 form parts of a string comprising a plurality of vehicles platooning, using autonomous vehicle following by means of the V2V communication. The lead vehicle is at the front of the string. In this example, a first 2 of the follower vehicles follows immediately behind the lead vehicle 1. A second 3 of the follower vehicles follows immediately behind the first follower vehicle 2. In this example, only three vehicles are shown, but the string could comprise more than three vehicles, or only two vehicles.

In the string each vehicle transmits wireless signals representative of the velocity and the acceleration of the transmitting vehicle, and vehicle features including the weight and dimensions of the transmitting vehicle. The vehicle immediately behind the respective transmitting vehicle receives said wireless signals from the transmitting vehicle. Thereby, in this vehicle platooning process, each vehicle, except the lead vehicle 1, is a receiving vehicle controlled to be at a relatively short distance from a transmitting vehicle immediately in front of the respective receiving vehicle.

It should be noted however, that the invention is applicable to situations where the distance between the vehicles is relatively large. The longitudinal control of the follower vehicle(s) may, instead of CACC, utilise Adaptive Cruise Control (ACC).

The V2V communication is also used for lateral vehicle control, as described closer below. The vehicle control system of the respective receiving vehicle controls brakes, a drivetrain, and a steering function of the receiving vehicle based on the wireless signals received from the respective transmitting vehicle.

It should be noted that in some embodiments, the vehicle control system of the respective receiving vehicle may control brakes, the drivetrain, and the steering function of the receiving vehicle based on the wireless signals received from a vehicle in front of the vehicle immediately in front of the respective receiving vehicle, e.g. from the lead vehicle at the front of the string, as an alternative to or in addition to wireless signals received from the vehicle immediately in front of the respective receiving vehicle.

The vehicles 1, 2, 3 each comprise a sensor arrangement 111, 211, 311, each comprising a radar sensor and a camera. Each control unit 102, 202, 302 is arranged to receive signals from the respective sensor arrangement 111, 211, 311. In alternative embodiments, the sensor arrangement could be a LIDAR sensor. It should be noted that the sensor arrangement can include a variety of combinations of sensors, and any number of sensors, such as a camera, lidar, radar, and/or an ultra-wideband transmitter or similar.

The sensor arrangement 111, 211, 311 may also be used to detect obstacles in a region in front of the respective vehicle. This region may include part of a lane in which the respective vehicle is travelling. Said region may also include parts of areas outside of the lane in which the respective vehicle is travelling. The region in which obstacles can be detected by the sensor arrangement 111, 211, 311 may include a part of a shoulder of the road on which the vehicles are travelling. Said region may include a part of a lane which is adjacent to the lane in which the respective vehicle is travelling. Such obstacles may be non-moving in relation to the road, or they may be moving. Also, by means of the sensor arrangement 111, 211, 311, the distance to, velocity of and acceleration of a vehicle in front of the respective vehicle may be determined. The sensor arrangement 111, 211, 311 may be arranged to detect objects on the side of the vehicle string. This may be useful to detect vehicles moving faster than the vehicle string, and driving in the same direction, in another lane, or on a motorway on-ramp.

With reference also to FIG. 2 an embodiment of a method according to the invention will be described. The lead vehicle 1 is moving along a lane of a road. The method comprises the follower vehicles 2, 3 following the lead vehicle 1. Thereby, all vehicles in the string are in the same lane.

The method comprises generating S1 operational data, as exemplified below, which is partly related to the operation of the lead vehicle 1. The operational data includes surroundings data, regarding the surroundings of the lead vehicle 1, generated by means of the sensor arrangement 111 on the lead vehicle 1. Thus, the surroundings data is generated by the lead vehicle. The operational data further includes road data, including one or more features of the road on which the vehicles are travelling. For example, the road data might include the information that the road is a motorway. The road data may be generated, by any of the vehicles 1, 2, 3, by the use of GNSS, map data and/or sensors in the respective sensor arrangement. The road data may include the number of lanes, and the intended direction of travel in the lanes. The operational data further includes lead vehicle driver data, regarding lead vehicle control actions initiated by a driver of the lead vehicle 1. The lead vehicle driver data may be generated by one or more devices arranged to register the movements of one or more driver control devices, such as a steering wheel, an accelerator pedal, a brake pedal, or a gear control device. The lead vehicle driver data may also be generated by one or more parameters handled by the lead vehicle control unit, such as a requested torque.

The method further comprises determining S2 based on the operational data whether to control the first follower vehicle 2 in a first mode or in a second mode. If the road is a motorway, with curves having high radii, and where there is normally a relatively large amount of space on the sides of the vehicle, it may be determined to control the follower vehicle 2 in the first mode.

Reference is made also to FIG. 3 showing the lead vehicle 1 and the first follower vehicle 2 from above. In FIG. 3, the distance between the lead vehicle 1 and the first follower vehicle is larger than in FIG. 1, and the orientations of the vehicles are exaggerated, in order to make the understanding easier of parameters used in the method according to this embodiment of the invention.

The first mode comprises determining S3 a position PL and a heading HL of the lead vehicle 1. In this example, this is done by GNSS equipment of the lead vehicle 1. The determined lead vehicle position and heading PL, HL, are sent to the first follower vehicle 2 via the V2V communication.

Substantially simultaneously to the determination of the lead vehicle position and heading PL, HL, a position PF and a heading HF of the follower vehicle 2 is determined S4, by the follower vehicle. The positions and the headings of the lead vehicle may be matched timewise with the positions and the headings of the first follower vehicle. This may be done, e.g. by repetitively updating the respective headings and positions, time stamping the updates, and matching positions and headings of one of the vehicles with positions and headings of the other of the vehicles, having the same time stamp. Alternatively, the position and heading of the first follower vehicle could be established when data about the position and heading of the lead vehicle is received by the first follower vehicle.

Subsequently to the establishments of the position PL and heading HL of the lead vehicle 1, and the position PF and heading HF of the first follower vehicle 2, the follower vehicle creates S5 a path for the follower vehicle 2 by fitting a curve C1 to said positions PL, PF and said headings HL, HF.

The curve fitting comprises creating the curve C1 so as to be tangential to each of said headings HL, HF at a respective of said positions PL, PF. The curve C1 is a polynomial of a degree of three. This allows creating a curve which bends in one direction in one portion of the path, and in another direction in another portion of the path. When the curve C1 is created the first follower vehicle is controlled S6 so as to move along the path established by the curve.

The determination S1 of operational data is continuously repeated. Upon updates of the operational data, the determination S2, whether to control the follower vehicle 2 in the first mode or in the second mode, is continuously repeated. While the follower vehicle 2 is in the first control mode, the steps S3, S4, S5 of determining the vehicle positions and headings, and establishing a path for the follower vehicle is continuously repeated. Thus, new paths are repetitively produced. When a new path is established, it replaces the preceding path in the control of the follower vehicle.

The control in the first mode may allow the follower vehicle to deviate from the exact path of the lead vehicle. This is beneficial, e.g. in case the lead vehicle, due to irrational human control actions of a driver of the lead vehicle, moves forth and back sideways within the lane. The follower vehicle may thereby avoid or reduce such sideways movements.

It should be noted that the positions and headings of the lead and follower vehicle must not be perfectly time synchronized for the method to work. Preferably, the lead vehicle was, at some point in time, in the lead vehicle position and heading used for the curve fitting. The lead vehicle position and heading used for the curve fitting may be a present vehicle position and heading, or a historical, although preferably recent, vehicle position and heading. The lead vehicle position, used for the curve fitting, is preferably in front of the follower vehicle. However, the lead vehicle position and heading used for the curve fitting may be older than the follower vehicle position and heading used for the curve fitting.

In this example, at an update of the operational data, the operational data becomes indicative of an obstacle ahead of the lead vehicle 1. The obstacle may be e.g. a large piece of debris, or a vehicle standing still, or travelling slower than the lead vehicle. The obstacle may be in the same lane as the lead vehicle is travelling. The updated operational data may be based on signals from the sensor arrangement 111 of the lead vehicle 1. The updated operational data is sent to the follower vehicle 2. Based on the updated operational data, the control unit of the follower vehicle 2 decides to change to controlling the follower vehicle 2 in the second mode.

Reference is made to FIG. 4. The second mode comprises determining S7 a plurality of positions PL, PLt-1, PLt-2 . . . of the lead vehicle 1 as the lead vehicle moves. The lead vehicle positions are repetitively established by the lead vehicle 1 by means of GNSS. As the lead vehicle positions PL, PLt-1, PLt-2 . . . are established, they are sent to the follower vehicle by means of V2V communication.

The follower vehicle establishes S8 a path for the follower vehicle 2 by fitting a curve C2 to at least some of the plurality of lead vehicle positions PL, PLt-1, PLt-2 . . . . The curve fitting could be done in any suitable manner, such as polynomial interpolation, curve splining, or least-squares fitting. When the curve C2 is created the follower vehicle is controlled S6 so as to move along the path established by the curve.

By changing to the second control mode, the follower vehicle 2 can follow the lead vehicle more exactly, when the latter maneuvers to avoid the obstacle. Such a maneuver may involve a lane change, which is exemplified below. Thereby, it is secured that also the follower vehicle will avoid the obstacle. When the vehicles have passed the obstacle, further updated operation data may allow for the follower vehicle to resume the control in the first mode.

In a further example, the operational data is indicative of a lane change of the lead vehicle 1, while the follower vehicle 2 is controlled in the first mode. Such operational data may include data based on signals from the sensor arrangement 111 of the lead vehicle 1. For example, the camera of the sensor arrangement may provide signals indicative of the lead vehicle starting to leave the lane. The operational data may also include data about a turn signal by the lead vehicle 1. The operational data is sent to the follower vehicle 2. Thereby, the method may involve determining, based on the operational data indicative of the lane change, to change to controlling the follower vehicle 2 in the second mode.

In yet further examples, the operational data is indicative of the lead vehicle 1 entering or driving on an off-ramp or an on-ramp at a motorway, on a narrow road, a road intersection, or in a roundabout, while the follower vehicle 2 is controlled in the first mode. Such operational data may include data based on signals from the sensor arrangement 111 of the lead vehicle 1, the sensor arrangement 211 of the follower vehicle, and/or GNSS and map data. The method may thereby involve determining, based on such operational data, to change to controlling the follower vehicle 2 in the second mode.

In this example, the first follower vehicle 2 may, for the control of the second follower vehicle 3, wholly or partially assume the role of the lead vehicle 1 in the control of the first follower vehicle 2. Thus, in some respects, the first follower vehicle 2 can be regarded as the lead vehicle in the control of the second follower vehicle 3.

For the control of the second follower vehicle 3, the operational data may wholly or partly be generated as described above. For example, the surroundings data and the lead vehicle driver data may be generated by the lead vehicle. The operational data is sent by V2V communication to the second follower vehicle 3.

The method comprises determining based on the operational data whether to control the second follower vehicle 3 in the first mode or in the second mode. The first mode may comprise determining a position and a heading of the lead vehicle 1, and sending the determined first follower vehicle position and heading to the second follower vehicle 3 via the V2V communication. Substantially simultaneously to the determination of the first follower vehicle position and heading, a position and a heading of the second follower vehicle 3 is determined, by the second follower vehicle 3. Subsequently to the establishments of the positions and headings of the lead vehicle and the second follower vehicle, the second follower vehicle 3 creates a path for the second follower vehicle 3 by fitting a curve to said positions and said headings. Alternatively, or in addition, the first mode may comprise determining a position and a heading of the first follower vehicle 2, and sending the determined first follower vehicle position and heading to the second follower vehicle 3 via the V2V communication. Substantially simultaneously to the determination of the first follower vehicle position and heading, a position and a heading of the second follower vehicle 3 may be determined, by the second follower vehicle 3. Subsequently to the establishments of the positions and headings of the first and second follower vehicles 2, 3, the second follower vehicle 3 may create a path for the second follower vehicle 3 by fitting a curve to said positions and said headings.

Based on updated operational data, the control unit of the second follower vehicle 3 may decide to change to controlling the second follower vehicle 3 in the second mode. The second mode comprises determining a plurality of positions of the lead vehicle 1 as the lead vehicle moves. As the lead vehicle positions are established, they are sent to the second follower vehicle 3 by means of V2V communication. The second follower vehicle 3 establishes a path for the second follower vehicle by fitting a curve to at least some of the plurality of lead vehicle positions. When the curve is created the second follower vehicle 3 is controlled so as to move along the path established by the curve. Alternatively, or in addition, the second mode may comprise determining a plurality of positions of the first follower vehicle 2 as the first follower vehicle moves. As the first follower vehicle 2 positions are established, they may be sent to the second follower vehicle 3 by means of V2V communication. The second follower vehicle 3 may establish a path for the second follower vehicle by fitting a curve to at least some of the plurality of first follower vehicle positions. When the curve is created the second follower vehicle 3 may be controlled so as to move along the path established by the curve.

Reference is made to FIG. 5. In some embodiments, paths may be determined in parallel according to both modes described above. This could mean that the path in the second mode is established while controlling the follower vehicle 2 so as to move along the path established in the first mode. For example, the method may comprise determining S3 a position and a heading of the lead vehicle, determining S4 a position and a heading of the follower vehicle, and subsequently establishing S5 a path for the follower vehicle by fitting a curve to said positions and said headings. Simultaneously, or in parallel, a plurality of positions of the lead vehicle may be determined S7 as the lead vehicle moves, and a path for the follower vehicle 2 may be established S8 by fitting a curve to at least some of the plurality of lead vehicle positions.

Operational data S1 is determined, e.g. as exemplified above. Based on the operational data, it is determined S2 whether to control the vehicle in the first mode. If it is determined to control the follower vehicle 2 in the first mode, the follower vehicle is controlled S61 so as to follow the path created S5 according to the algorithm of the first mode. If it is determined S2 to control the follower vehicle 2 in the second mode, the follower vehicle is controlled S62 so as to follow the path created S8 according to the algorithm of the second mode. Thereby, the path estimation in one of the modes is actively used, while the path estimation in the other mode is passive.

In some embodiments, the determination whether to control the follower vehicle in the first mode or the second mode may be based on a difference between the paths generated in the modes. For example, if the path established in the first mode differs from the path established in the second mode by more than a predetermined threshold difference, the path established in the second mode may be selected. Said difference may be derived by a least square calculation of distances between lateral positions of the paths. Alternatively, the difference may be an absolute distance between lateral positions of the paths.

Reference is made to FIG. 6 and FIG. 7. FIG. 6 shows an example of a situation, where a string for vehicle platooning is to be initiated. A vehicle 1 is to become the lead vehicle of the string, i.e. the vehicle travelling in the front of the string. The lead vehicle 1 is standing still. The position of the lead vehicle is determined S3. The heading of the lead vehicle was established S3 when the lead vehicle parked in the position in which it is standing still. The heading is stored in a memory accessible to the control unit of the lead vehicle. The lead vehicle heading, and the lead vehicle position is sent, via V2V communication, to another vehicle 2, which is to become a follower vehicle in the string. The position and heading of the follower vehicle 2 are established S4. Subsequently a path for the follower vehicle 2 is established by fitting a curve C1 to said positions and said headings. Thereupon, the follower vehicle 2 is controlled so as to move along the established path. Thereby the follower vehicle may park behind the lead vehicle, before the platooning starts.

With reference to FIG. 8 and FIG. 9, an example of a method according to a further aspect of the invention will be described. In this example, a follower vehicle (e.g. vehicle 2 in FIG. 1) follows a lead vehicle (e.g. vehicle 1 in FIG. 1). The lead vehicle and the follower vehicle form parts of a string comprising a plurality of vehicles platooning, using autonomous vehicle following by means of the V2V communication. In this example, the lead vehicle is controlled manually by a person, i.e. a driver. The follower follows the lead vehicle using autonomous vehicle following. The method comprises establishing, in a first control mode of the follower vehicle, a path for the follower vehicle to follow the lead vehicle.

The method further comprises generating S1 environmental data which is related to the environment of the lead vehicle. In this example, the environmental data comprises speed limit data. The speed limit data may be provided by means of map data, and/or sensor data, e.g. as exemplified above. The speed limit data may be determined by the follower vehicle. The speed limit data in this example is the speed limit along a stretch of the road, on which the vehicles are travelling. In FIG. 8, the horizontal axis indicates the distance along the road. The speed limit along the stretch of the road is indicated by the line SL in FIG. 8. According to the speed limit data, at a location L along the road, the speed limit is reduced, in this example from 70 km/h to 60 km/h.

Based on the generated environmental data, an expected behaviour of an operational parameter of the lead vehicle is determined S2. Said expected behaviour may be determined by the follower vehicle. In this example, the lead vehicle operational parameter is the acceleration of the lead vehicle. In this example, the expected behaviour of the lead vehicle acceleration is the expected behaviour of the lead vehicle acceleration along the stretch of the road.

Determining the expected behavior of the lead vehicle operational parameter comprises determining, at each location along the road, an interval of the operational parameter. For this, a nominal acceleration profile, indicated in FIG. 8 by the line NAP, is determined. The nominal acceleration profile NAP may be determined by means of a driver model, and a model of the lead vehicle. The nominal acceleration profile NAP may indicate how a nominal driver would control the lead vehicle at the change of the speed limit. To take into account that the acceleration profile may differ from one driver to another, within a limited, normal, or acceptable, driver control spectrum, an acceleration acceptance span is formed around the nominal acceleration profile NAP. As indicated in FIG. 8, the acceleration acceptance span is formed by an upper acceleration profile limit UAP, above the nominal acceleration profile NAP, and a lower acceleration profile limit LAP, below the nominal acceleration profile NAP. Thus, the upper acceleration profile limit UAP and the lower acceleration profile limit LAP provides, at each location along the stretch of the road, an interval of the lead vehicle acceleration, forming an expected behavior of the lead vehicle acceleration.

An actual behaviour of the lead vehicle operational parameter is determined S3. Said actual behaviour may be determined by the follower vehicle. In this example, the actual acceleration of the lead vehicle is determined. This may be done as exemplified above, e.g. by the lead vehicle actual acceleration being communicated to the follower vehicle by the V2V link, or being measured with a sensor on the follower vehicle. The actual acceleration, at each location of the stretch of the road, is indicated by the line AA in FIG. 8.

The determined actual behaviour of the lead vehicle operational parameter is compared S4 to the determined expected behaviour of the lead vehicle operational parameter. In this example, the determined actual acceleration AA of the lead vehicle is compared to the determined acceleration acceptance span UAP, LAP. The comparison comprises repetitively determining whether the actual acceleration AA is within the interval formed by the acceleration acceptance span UAP, LAP.

Based on said comparison S4 the follower vehicle determines S5 whether to continue in first control mode, or in a second control mode, differing from the first control mode. In this example, if the actual acceleration AA is within the interval formed by the acceleration acceptance span UAP, LAP, no change in the follower vehicle control mode is effected, i.e. put into action. In the example in FIG. 8, the actual acceleration AA is within the interval, formed by the acceleration acceptance span UAP, LAP, throughout the stretch of the road. However, if the actual acceleration AA is outside of the interval formed by the acceleration acceptance span UAP, LAP, a change in the follower vehicle control mode is effected.

With reference to FIG. 10, a further example of a method according to a further aspect of the invention will be described. In this example, the generated environmental data, which is related to the environment of the lead vehicle, comprises the curvature of the road on which the lead vehicle is travelling, herein also referred to as road curvature data. The road curvature data may be determined by the follower vehicle. The road curvature data may be determined by means of road surface markings at the lead vehicle. The road surface marking may be detected by means of one or more sensor on the lead vehicle, such as a camera, and/or a LIDAR sensor. The sensor may be provided on the lead vehicle. The sensor data, or the road curvature data, may be communicated to the follower vehicle via the V2V link. The road curvature data may alternatively, or in addition, be based on map data.

In FIG. 10, the horizontal axis indicates the distance along the road. Based on the generated road curvature data, an expected behaviour of an operational parameter, in the form of the lead vehicle steering angle, is determined. Said expected behaviour, of the lead vehicle steering angle, may be determined by the follower vehicle. Alternatively, the expected behaviour may be determined by the lead vehicle. The lead vehicle steering angle expected behavior may be determined by means of a driver model, and/or a model of the lead vehicle.

Determining the expected behavior of the lead vehicle steering angle comprises determining, at each location along the road, an interval of the steering angle. For this, a nominal steering angle profile, indicated in FIG. 10 by the line NSP, is determined. The nominal steering angle profile NSP may indicate how a nominal driver would steer the lead vehicle along the road. To take into account that the steering angle profile may differ from one driver to another, within a limited, normal, or acceptable, driver control spectrum, a steering angle acceptance span is formed around the nominal steering angle profile NAP. As indicated in FIG. 10, the steering angle acceptance span is formed by an upper steering angle profile limit USP, above the nominal steering angle profile NSP, and a lower steering angle profile limit LSP, below the nominal steering angle profile NSP. Thus, the upper steering angle profile limit USP and the lower steering angle profile limit LSP provides, at each location along the stretch of the road, an interval of the lead vehicle steering angle, forming an expected behavior of the lead vehicle steering angle.

An actual behaviour of the lead vehicle steering angle is determined. Said actual behaviour may be determined by the lead vehicle, and communicated to the follower vehicle via the V2V link. The actual steering angle, at each location of the stretch of the road, is indicated by the line AS in FIG. 10.

The determined actual steering angle AS of the lead vehicle is compared to the determined steering angle acceptance span USP, LSP. The comparison comprises repetitively determining whether the actual steering angle AS is within the interval formed by the steering angle acceptance span USP, LSP.

Based on said comparison the follower vehicle determines whether to continue in first control mode, or in a second control mode, differing from the first control mode. In this example, if the actual steering angle AS is within the interval formed by the steering angle acceptance span USP, LSP, no change in the follower vehicle control mode is effected. In the example in FIG. 10, the actual steering angle AS is, until the lead vehicle reached the location L1, within the interval, formed by the steering angle acceptance span USP, LSP.

Between the location L1 and L2, the actual steering angle AS is outside of the interval formed by the steering angle acceptance span USP, LSP. Therefore, a change in the follower vehicle control mode is effected.

At the location L2, the actual steering angle AS returns inside the interval formed by the steering angle acceptance span USP, LSP. Thereupon, a further change in the follower vehicle control mode is effected.

It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims. 

The invention claimed is:
 1. A method for a follower vehicle following a lead vehicle in a first follower control mode of the follower vehicle, the method comprising: establishing a path for the follower vehicle to follow the lead vehicle; generating environmental data which is related to the environment of the lead vehicle; determining, by a control unit, based on the generated environmental data, an expected behaviour of an operational parameter of the lead vehicle; determining, by the control unit, an actual behaviour of the lead vehicle operational parameter; comparing, by the control unit, the determined expected behaviour of the lead vehicle operational parameter and the determined actual behaviour of the lead vehicle operational parameter; determining, by the control unit, based on the comparison, whether to continue in the first follower control mode of the follower vehicle, or continue to follow the lead vehicle in a second follower control mode of the follower vehicle, differing from the first follower control mode, wherein the first follower control mode further comprises: determining, by the control unit, a position and a heading of the lead vehicle; determining, by the control unit, a position and a heading of the follower vehicle; establishing, by the control unit, a path for the follower vehicle by fitting a curve to the positions and the headings; and controlling, by the control unit, the follower vehicle to move along the established path.
 2. The method of claim 1, wherein: determining the expected behavior of the lead vehicle operational parameter comprises determining an interval of the operational parameter; and comparing, the determined expected behaviour of the lead vehicle operational parameter and the determined actual behaviour of the lead vehicle operational parameter, comprises determining whether an actual value of the operational parameter is within the operational parameter interval.
 3. The method of claim 1, wherein the environmental data comprises speed limit data.
 4. The method of claim 1, wherein the environmental data comprises a curvature of the road on which the lead vehicle is travelling.
 5. The method of claim 1, wherein the lead vehicle operational parameter is a steering angle of the lead vehicle.
 6. The method of claim 1, wherein the curve fitting comprises creating the curve so as to be tangential to each of the headings at a respective of the positions.
 7. The method of claim 1, wherein the curve is a polynomial of a degree of at least three.
 8. The method of claim 1, wherein the lead vehicle is standing still, when the path for the follower vehicle is established.
 9. The method of claim 1, wherein the second follower control mode comprises determining a plurality of positions of the lead vehicle as the lead vehicle moves, and establishing a path for the follower vehicle by fitting a curve to at least some of the plurality of lead vehicle positions.
 10. The method of claim 1, further comprising generating operational data comprising at least one of surroundings data, regarding the surroundings of the lead vehicle and/or the follower vehicle, road data, including at least one feature of a road on which the vehicles are travelling, and at least one value of at least one operational parameter of the lead vehicle.
 11. The method of claim 10, wherein at least one part of the operational data is generated by the lead vehicle.
 12. The method of claim 10, wherein the operational data includes surrounding data generated by the lead vehicle.
 13. The method of claim 10, wherein: the operational data is indicative of a change of a lead vehicle control strategy, from a first lead vehicle control strategy to a second lead vehicle control strategy, while the follower vehicle is controlled in the first follower control mode; and the method further comprises determining, based on the operational data indicative of the lead vehicle control strategy change, to change to controlling the follower vehicle in the second follower control mode.
 14. The method of claim 10, wherein the operational data includes at least one value of at least one operational parameter of the lead vehicle exceeding or being below a respective predetermined threshold value.
 15. The method of claim 10, wherein the operational data includes data on a combination of substantially simultaneous events.
 16. The method of claim 10, wherein the operational data includes a pattern of a plurality of values of a lead vehicle operational parameter.
 17. The method of claim 10, wherein: the operational data is indicative of an obstacle ahead of the lead vehicle, while the follower vehicle is controlled in the first follower control mode; and the method further comprises determining, based on the operational data indicative of the obstacle, to change to controlling the follower vehicle in the second follower control mode.
 18. The method of claim 10, further comprising establishing the path in the second follower control mode while controlling the follower vehicle so as to move along the path established in the first follower control mode. 